Fixes to improve readability and gas usage

[kyriediculous]

• Use OwnableUpgradeable instead of custom modifier
• Fix typo
• Use named struct params upon initialisation
• Initialise checkpoints when registering a protocol
• improve readability and gas usage of depositChecker
  • There's no need to store block.timestamp in a variable. MSTORE is at least 3 gas, MLOAD is also at least 3 gas while the TIMESTAMP opcode is 2 gas
  • The call to check the balance only needs to take place if the interval to check has elapsed
  • No need to call abi.encode with empty arguments. The memory is already initialized with a zero value bytes array because of named function params.

[height]

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